This invention relates to the use of a device for the corrosion protection of a string of metal tubes. More particularly, the device of this invention will be used as a tubing joint in a production string of tubes or pipes, or casings in oil and gas production wells.
Oil and gas wells typically have corrosion problems because the metal parts, usually iron or steel, are exposed to corroding agents. Ground water generally presents the large corrosive problem. The corrosion-problem is particularly accute in producing oil wells because the components in the well are subjected to corrosive environmental conditions. If the metal tubing and pipes are not replaced before corrosion perforations are formed, then infiltration of water and silt will occur which will affect oil and gas production. It has been found that the corrosion in wells occurs on the inside and outside walls of the casing. Three methods have been used to combat this corrosion. The methods include: coatings; the use of inhibitors; and alloy metals. Coatings have included the use of baked-on phenolics, air-dryed and baked epoxy resins, and galvanizing. Each of these techniques have cost and physical attribute limitations.
Zinc has been used as a corrosion inhibiting agent in several different techniques. An early approach to to corrosion problem is shown in the patent to Mills, U.S. Pat. No. 1,646,736, Electrochemical Means For Preventing Corrosion, where the use of a collar containing zinc is placed in close proximity to the metal surface to be protected. Another technique is shown in the patent to Mills, U.S. Pat. No.1,705,197, Electrochemical Means for Protecting the Interior of Pipes Against Corrosion, where an outer shell of steel encloses an inner casting of zinc. A third technique is shown in the patent to Ewing, U.S. Pat. No. 3,251,427, Protection Of Drill Pipe, where zinc rings are in intimate contact with the external surface of the pipe.
It would be desirable to be able to increase the corrosion protective qualities of the metal production string by using a sacrificial metal which does not project into the bore of the tube or cause any projection or increase in the outside diameter of the tube.